Sometimes people like to panic when their computer's resources seem to be maxed out. While CPUs and hard disks may suffer from high usage, RAM doesn't necessarily slow down your computer when it appears to be running low.

When you have a bunch of programs open, your computer's running slowly, and your RAM is maxed out, you're experiencing the bad side of high memory usage. Chances are your computer is caching to disk instead of RAM and that's just slow in general. If this is the case, you may need more RAM. That said, your RAM may still appear to be in full use even if your computer is running just fine. This is good, as your computer is simply filling your RAM up with cache files. How-To Geek explains:

Whether your RAM is full of cached files or completely empty, it's all available for programs that really need it. Cached data in your RAM is marked as low-priority, and it's instantly discarded as soon as the memory is needed for something else. Because this data can be instantly discarded when necessary, there's no disadvantage to using the RAM for cache. (The one potential disadvantage is users who don't understand what's going on becoming confused.)

Empty RAM is useless. It's not any faster for the computer to write data to empty RAM, nor does empty RAM use less power. In fact, assuming you're launching a program that may already be present in your RAM's file cache, programs will load much faster when your RAM is used rather than when it's empty.

Basically, don't worry if your RAM is full unless your computer's running slow. For an in-depth look at the subject, read the full post over on How-To Geek.